Hydraulic control apparatus for hydraulic-lift end gates of moving vans and the like

ABSTRACT

The apparatus controls at least one double-acting hydraulic consumer, such as a hydraulic-lift end gate of a moving van, or the like. The apparatus includes at least one valve member movable between first operative, second operative and neutral positions to thereby respectively connect a first fluid-conveying line of the consumer with a supply conduit which is connected to a source of pressurized fluid, with a return conduit which is connected to a tank, and to seal the first fluid-conveying line of the consumer from the supply and return conduits. The valve member of the control valve also controls the flow of fluid in a control conduit for a switchover valve which opens in response to fluid flow in the control conduit to provide a path for the flow of pressurized fluid from the supply conduit into a second fluidconveying line of the consumer. A pressure-regulating unit is connected between the outlet of the switchover valve and the tank, and is operative for regulating the pressure of fluid in the second fluid-conveying line of the double-acting consumer. The pressure-regulating unit is provided in the form of a flow restrictor connected between the outlet of the switchover valve and the tank and a check valve connected parallel to the flow restrictor with such an orientation as to permit flow of fluid from the tank into the second fluid-conveying line of the doubleacting consumer.

Herrmann Oct. 7, 1975 HYDRAULIC CONTROL APPARATUS FOR HYDRAULIC-LIFT ENDGATES OF MOVING VANS AND THE LIKE Inventor: Walter Herrmann, Vaihingen,Enz,

Germany Assignee: Robert Bosch G.m.b.H., Stuttgart,

Germany Filed: Dec. 12, 1973 Appl. No.: 422,596

[30] Foreign Application Priority Data Jan. 13, 1973 Germany 2301607[52] US. Cl. 60/433; 60/484; 91/16; .91/52; 91/165; 91/414; 91/441;91/463 [51] Int. Cl. F16D 31/02 [58] Field of Search ..91/469, 16,18,52, 441, 91/165, 463; 60/433, 474, 478, 481, 484, 477

[56] References Cited UNITED STATES PATENTS 2,797,550 7/1957 Stelzer60/481 X 3,130,548 4/1964 Hunt 60/478 X 3,321,909 5/1967 Gordon 60/477 X3,415,057 12/1968 Rosenberg 91/16 X 3,455,209 7/1969 Preston et a191/445 X 3,604,205 9/1971 Geselbracht et a1... 60/477 X 3,761,123 9/1973Neill et al. 91/452 X 3,854,289 12/1974 Herrmann et al 60/484 X PrimaryExaminer-Martin P. Schwadron Assistant Examiner-Abraham HershkovitzAttorney, Agent, or Firm-Michael S. Striker [57] ABSTRACT The apparatuscontrols at least one double-acting hydraulic consumer, such as ahydraulic-lift end gate of a moving van, or the like. The apparatusincludes at least one valve member movable between first operative,second operative and neutral positions to thereby respectively connect afirst fluid-conveying line of the consumer with a supply conduit whichis connected to a source of pressurized fluid, with a return conduitwhich is connected to a tank, and to seal the first fluid-conveying lineof the consumer from the supply and return conduits. The valve member ofthe control valve also controls the flow of fluid in a control conduitfor a switchover valve which opens in response to fluid flow in thecontrol conduit to provide a path for the flow of pressurized fluid fromthe supply conduit into a second fluid-conveying line of the consumer. Apressure-regulating unit is connected between the outlet of theswitchover valve and the tank, and is operative for regulating thepressure of fluid in the second fluid-conveying line of thedouble-acting consumer. The pressure-regulating unit is provided in theform of a flow restrictor connected between the outlet of the switchovervalve and the tank and a check valve connected parallel to the flowrestrictor with such an orientation as to permit flow of fluid from thetank into the second fluid-conveying line of the double-acting consumer.

5 Claims, 1 Drawing Figure HYDRAULIC CONTROL APPARATUS FORHYDRAULIC-LIFT END GATES .OF MOVING VANS AND THE LIKE BACKGROUND OF THEINVENTION positions to thereby respectively connect a firstfluidconveying line of a consumer with a supply conduit which isconnected to a source of pressurized fluid, with a return conduit whichis connected to a tank, and to seal the first fluid-conveying line ofthe consumer from the supply and return conduits. The at least one valvemember of the control valve controls the flow of fluid in a controlconduit for a switchover valve which opens in response to fluid flow inthe control conduit to provide a path for the flow of pressurized fluidfrom the supply conduit into a second fluid-conveying line of thedouble-acting consumer. In the arrangement being referred to,pressure-regulating means is connected between the outlet of theswitchover valve and the tank and is operative for regulating thepressure of fluid in the second fluid-conveying line of thedouble-acting consumer, and specifically is operative for keeping thepressure furnished to the second fluid-conveying line of thedouble-acting consumer lower than the pressure furnished to the firstfluid-conveying line of the doubleacting consumer.

In the arrangement being referred to, the pressureregulating means wasprovided in the form of a pressure-limiting valve connected between theoutlet of the switchover valve and the tank and operative for limitingthe pressure in the second fluid-conveying line of the double-actingconsumer to a predetermined value.

Provision of such a pressure-limiting valve connected between the outletof the switchover valve and the tank does reliably limit the pressure inthe second fluidconveying line of the double-acting consumer. However,the use of a pressure-limiting valve is relatively expensive,particularly in the context of a hydraulic control apparatus ofrelatively simple construction and comprised of only a few valves.

SUMMARY OF THE INVENTION It is the general object of the invention toprovide a hydraulic control apparatus similar to the apparatus referredto above, but of simpler and less expensive construction.

More particularly, it is an object of the invention to provide ahydraulic control apparatus similar to the apparatus referred to above,but using simpler and les expensive means in place of thepressure-limiting valve referred to above.

Still more particularly, it is an object of the invention to provide ahydraulic control apparatus similar to the apparatus referred to above,but using instead of the pressure-limiting valve referred to abovedifferent means having an inherent operation different from the Suchsimilarity of action can exist notwithstanding viscosity-andvolume-dependent pressure oscillations.

These objects, and others which will become more understandable from thefollowing description of a preferred embodiment, can be met according toone advantageous concept of the invention by replacing thepressure-limiting valve referred to above with a parallel combination ofasimple flow restrictor and a simple check valve, this parallelcombination being connected between the outlet of the switchover valveand the tank, and the check valve having such an orientation as topermit free flow of fluid from the tank through the check valve and intothe second fluid-conveying line of the double-acting consumer device.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE depicts an exemplaryembodiment of the invention. I

DESCRIPTION OF THE PREFERRED EMBODIMENTS The single FIGURE illustrates ahydraulic control apparatus for two discrete consumers in the form ofcylinders 12, 13 which impart various movements to the end gate G of atruck, station wagon or an analogous automotive vehicle. The cylinder 12is of the double-acting type and serves to pivot the gate G between openand closed positions (arrow 9), and the cylinder 13 is a double-actinghydraulic jack which can raise the gate G (arrow 10) from a lower endposition in which the gate is ready to be pivoted to its closedposition. The gate G ordinarily descends under its own weight when thecontrol apparatus 120 allows fluid to escape from the lower chamber 42of the cylinder 13.

The control apparatus 120 comprises a block-shaped housing 14 whichincludes a connecting unit 121 adapted to be secured to the dashboard orto another part of the vehicle, an end unit 18, and two identicalcontrol valves 16, 17, here shown in the form of directional controlvalves. The valves 16 and 17 may be constructed as shown in FIG. 5 ofcommonly owned US. Pat. application Ser. No. 395,372 of Hermann et al.,filed Sept. 7, 1973, now US. Pat. No. 3,854,289, the disclosure of whichis incorporated herein by reference.

The control valves 16, 17 are connected in parallel between a supplyconduit 19 for pressurized oil or an other hydraulic fluid and a returnconduit 21 for hydraulic fluid. The valve members of each of the controlvalves 16, 17 are movable between central or neutral positions 22 (whichare established by suitable resilient biasing means) and two operativepositions 24, 25.

When in the neutral positions 22, the valve members of the control valve17 seal the conduits 19, 21 from a first fluid-conveying line orconsumer line 39 which is connected with the lower chamber 40 of thecylinder 12. When in the neutral position 22, the valve members of thecontrol valve 16 seal the conduits 1 9, 21 from a first fluid-conveyingline or consumer line 41 which is connected with the lower chamber 42 ofthe cylinder 13. When in the first operative position 24, the valvemembers of the control valves 16, 17 respectively connect the supplyconduit 19 with the consumer lines 41, 39. When in the second operativepositions 25, the valve members of the control valves 16, 17respectively connect the return conduit 21 with the consumer lines 41,39. The valve members of the control valves 16, 17 are movable bydiscrete mechanical actuating means 26, and each actuating means 26comprises a cam or trip 27 for a normally open limit switch 28. When alimit switch 28 is closed (in the first operative positions 24 of therespective valve members), an electric motor 36 or an analogous primemover drives a pump 35 which constitutes a source of pressurizedhydraulic fluid.

The connecting unit 121 supports or embodies a pressure relief valve 29which opens automatically when the pressure of fluid in the supplyconduit 19 rises to a predetermined maximum permissible value and thenallows pressurized fluid to flow from the supply conduit 19 into thereturn conduit 21 and from there into a reservoir or tank 37.Furthermore, the connecting unit 121 supports or comprises aconventional switchover valve 32 which is connected to the supplyconduit 19 by a bypass conduit 31. A control conduit 33 connects thebypass conduit 31 with the return conduit 21, and the flow of fluidtherein is regulated by the control valves 16 and 17. A portion of thecontrol conduit 33 extends through the unit 18 of the housing 14. Whenthe control conduit 33 is allowed by control valves 16 and 17 to conveyfluid from the conduit 31 to the conduit 21, the flow of fluid incontrol conduit 33 maintains the switchover valve 32 in open position.Specifically, the illustrated compression spring normally biases thevalve member of switchover valve 32 to valve-closing position. When aflow of fluid is established in control conduit 33, the pressuredifference across restrictor 34 results in a net force opposing thebiasing force of the compression spring and moving the valve member ofvalve 32 to open position.

The consumer line 39 admits pressurized hydraulic fluid to the lowerchamber 40 of the cylinder 12 when the piston rod 12a is to pivot thegate G to its closed position. The upper chamber 46 of the cylinder 12then discharges fluid by way of a second fluid-conveying or working linewhich is connected to an additional conduit 72. The latter isconnectable to the bypass conduit 31 by the switchover valve 32. Theupper chamber 47 of the cylinder 13 is likewise connected to theadditional conduit 72. The chamber 47 discharges fluid when the chamber42 of the cylinder 13 receives pressurized fluid for the purpose ofmoving the gate G from the lower to the upper end position.

The operation of the illustrated control arrangement is as follows:

It will initially be assumed that the end gate G is in the elevated andclosed position, with the pistons 12b and 13b accordingly in theirrespective upper positions.

Firstly, it is desired to cause the end gate G to pivot downwardly toassume an approximately horizontal orientation. This can be effected ineither one of two different ways.

As the first possibility, the end gate G can be caused to swingdownwards under its own weight. To effect this, the actuator 26 of valve17 is moved leftwards, causing the one or more valve members in valve 17to assume the second operative position 25. In this valve position, thefluid-conveying line 39 of the cylinder 12 is made to communicate withthe return conduit 21, and fluid will be expelled from lower cylinderchamber 40, as piston 12b descends under the weight of the end gate G.As the piston 12b descends and expels fluid from chamber 40, the upperchamber 46 of cylinder 13 will become filled with fluid drawn up fromtank 37 by the force of simple suction via conduit 21, conduit 122,check valve 124 and also to some extent restrictor 123, and via conduit72. Under these circumstances, the valve members of valve 17 will be insecond operative position 25 and those of valve 16 in the neutralposition 22, and accordingly flow of fluid through control conduit 33will not be blocked. However, there is in fact no flow of fluid throughcontrol conduit 33, because the pump 35 has not been activated, therebeing no need for activation of the pump when the end gate G is made toswing downwards simply under its own weight. With no flow of fluidthrough control conduit 32, no pressure difference will develop acrossrestrictor 34, and accordingly no net pressure opposing the force ofbiasing spring will open switchover valve 32. Therefore, switchovervalve 32 will remain closed if the end gate G is made to swing downsolely under its own weight.

It may happen that downward swinging of the end gate G solely under itsown weight, in the manner just described, will not be possible. Forexample, if the van provided with the hydraulic-lift end gate G isparked on a downward incline, the end gate G may be so disposed that itsown weight will tend to maintain it in closed position, instead ofcausing it to swing downwards as would be the case if the van wereparked on a horizontal surfacce or on an upward incline. To effect thedesired downward swinging of the end gate G under such circumstances,the following must be done:

The actuator 26 of valve 17 will be pushed in leftwards direction, asjust described, to thereby move the valve members of valve 17 to thesecond operative position 25 thereof. If, because of the just-mentionedinclination of the van, the end gate G does not swing downwards, thenthe actuator 26 is pushed leftwards a further distance. This causesswitch 28 to be pushed by camming surface 27 towards the respective pairof electrical contacts. When these electrical contacts are bridged, theelectromotor 36 becomes energized, and the pump 35 begins to pump fluidinto the supply conduit 19. accordingly As a result, pressurized fluidbegins to flow through supply conduit 19, through bypass conduit 31 andalong control conduit 33, back to tank 37 via return conduit 21. Theflow of fluid through control conduit 33 creates a pressure differenceacross flow restrictor 34. This pressure difference opposes the biasingforce of compression spring 42 and moves the valve member of switchovervalve 32 to the valve-opening position. As a result, the pressurecreated by operation of pump 35 is communicated to some extent tocylinder chamber 46, via bypass conduit 31, switchover valve 32 andfluid-conveying line 72. It will be noted that the pressure in conduit72 and aaccordingly in cylinder chamber 46 will be limited by provisionof the return-flow conduit 122 which connects the outlet port of valve32 to the return conduit 21. However, the pressure in line 72 will notfall to zero, because the restrictor 123 in conduit 122 evidently doesnot permit unthrottled flow of fluid to tank 37. On the other hand, thediversion of fluid to tank 37 via the restrictor 123 and conduit 122causes the pressure in line 72 to be lower than the pressure associatedwith the pressure-limiting valve 29. This lowering of the pressure inline 72 in this manner is appropriate, because evidently only arelatively small force is required to cause the end gate G to swingdownwards, the required force being considerably lower than the forcerequired to cause the end gate G to swing upwards. In any event, the endgate G does swing downwards, not solely because of its own weight butinstead because of the positive pressure pushing piston 12b downwards.

With the end gate G now swung down to open position, the end gate willfor example be flush with the floor of the cargo compartment of the van,to permit cargo to be rolled or slid onto the horizontal end gate.Further movement of the piston 12b is not now required, and accordinglythe valve members of valve 17 will be returned to their neutralpositions 22.

The cargo having been rolled or slid onto the end gate, it will now bedesired to lower the end gate to the street level, for example, so thatthe cargo can be rolled or slid off the end gate and onto the street. Toaccomplish such lowering of the end gate, the actuator 26 of valve 16will be moved in leftwards direction, to move the valve members of valve16 to the second operative position 25. This establishes communicationbetween compartment 42 of cylinder 13 and the return conduit 21.Accordingly, the end gate G descends under its own weight and under theweight of any supported cargo, lowering piston 13b and expellingpressure fluid from compartment 42. The lowering of piston 13b solely asa result of the weight of the end gate and any supported cargo isexactly analogous to the lowering of piston 12b solely under the weightof the end gate, as described above. Accordingly, it will simply benoted that when the end gate is lowered in this manner, the switch 28associated with valve 17 will not activate the pump motor 36, and theswitchover valve 32 will be closed. As the piston 13b descends, theupper compartment 47 of cylinder 13 becomes filled with pressure fluidsucked up from tank 37 via return conduit 21, conduit 122, check valve124 and to some extent restrictor 123, and via conduit 72.

Under some circumstances, it may happen that the lowering of thehorizontally disposed end gate under its own weight plus the weight ofany supported cargo will not be satisfactory. It may be desired that anadditional force push down the end gate towards the street level, forexample to cause the end gate to lie as flat as possible on soft anduneven ground. To accomplish this, the following is done.

After the actuator 26 of valve 16 has been moved in leftwards direction,to move the valve members of valve 16 to position 25, the actuator 26 ispushed a small additional distance, to cause the camming surface 27 topush switch 28 into engagement with the respective pair of electricalcontacts. This energizes the pump motor 36, and the pump 35 will pumppressure fluid from the tank 37 into the supply conduit 19. Pressurewill be communicated to bypass conduit 31, but will be limited to thevalue associated with pressure-limiting valve 29. Fluid will flowthrough control conduit 33, creating the aforedescribed pressure dropacross restrictor 34, which opens valve 32. As a result, pressure fluidwill flow from bypass conduit 31 through valve 32 and conduit 72 intothe upper chamber 47 of cylinder 13, positively forcing the piston 13adownwards. The connection of the outlet port of valve 32 to the returnconduit 21 via restrictor 123 and conduit 122 makes for a pressure inline 72 and chamber 47 which is lower than the pressure established bypressure-limiting valve 29 in bypass conduit 31. This is appropriate,because maximum fluid pressure would not be required for the lowering ofthe end gate G, even in the situation where the weight of the end gateplus any cargo is not sufficient for a particular situation.

Once the horizontally oriented end gate G has been lowered to groundlevel, the actuator 26 will be moved rightwards to cause the valvemembers of valve 16 to assume the neutral position 22, inasmuch asfurther movement of piston 13b will not be required or desired at thistime.

After the cargo on the end gate has been rolled or slid off the end gateand onto the street, it may be desired to roll or slide different cargofrom the street onto the end gate. This done, it will be desired toraise the end gate to a level flush with the floor of the cargocompartment of the van, so that the new cargo can be rolled or slid ontothe floor of such cargo compartment. To do this, the following is done:

Activator 26 of valve 16 will be moved in rightwards direction, to movethe valve members of valve 16 to first operative position 24. Thecamming surface 27 of the activator 26 will immediately effect closingof switch 28 and energization of the pump motor 36. Pres sure fluid willbe pumped through supply conduit 19 and the check valve associated withvalve 16, and through consumer line 41 into compartment 42 of cylinder13, raising piston 13b and accordingly raising the end gate G.

When the valve members of valve 16 are in position 24, fluid flowthrough control conduit 33 is blocked, and accordingly switchover valve32 remains blocked. Accordingly, the pressure of fluid in supply conduit19 will be limited only by the acction of the pressurelimiting valve 29.

As the piston 13b is pushed upwards in this manner, the fluid in theupper cylinder chamber 47 will be expelled through conduit 72,restrictor 123 and conduit 122, into the return conduit 21 leading tothe tank 37.

When the end gate has been raised to a level flush with the cargocompartment floor, the activator will be moved in leftwards direction torestore the valve members of valve 16 to neutral position 22, sincefurther movement of piston 13b will not be required or desired at thistime. Operation of the pump 35 will cease. The cargo supported on thehorizontally disposed end gate will be rolled or slid into the cargocompartment of the van.

Finally, it will be desired to cause the end gate, now horizontallydisposed at the level of the cargo compartment floor, to swing upwardsto its closed position. To accomplish this, the activator 26 of valve 17is moved rightwards, to move the valve members of valve 17 to the firstoperative position 24. The cam surface 27 of the activator 26 of valve27 immediately closes the respective switch 28 and energizes the pumpmotor 36. Pressure fluid is pumped into the lower cylinder chamber 40via supply conduit 19, valve 17 and consumer line 39, forcing piston 12bupwards. When the end gate G reaches its closed position, the activator26 of valve 17 is moved rightwards, to move the valve members of valve17 back to neutral position 22, simultaneously terminating operation ofpump 35.

This is the complete cycle of operation of the illustrated arrangement.However, it is noted that it would of course be possible toalternatively effect lowering of the end gate simultaneously with thedownward swinging thereof, and to effect raising of the end gatesimultaneously with the upward swinging thereof, in which case the twoactivators 26 could be operated in unison.

An important advantage of the illustrated arrangement is the use of theparallel combination of the flow restrictor 123 and the check valve 124.When pressure fluid is pumped via line 72 into one of the upper cylinderchambers 46, 47, the provision of the restrictor 123 reduces the workingpressure, relative to the pressure employed to raise the pistons 12b and13b. In this sense the restrictor 123 performs to some extent thefunction of a pressure-limiting valve. However, it will be appreciatedby persons skilled in the art that the use of a simple flow restrictor123 in this context, instead of a pressure-limiting valve, isconsiderably more simple and economical, reducing both the initial andmaintenance cost of the arrangement. The provision of the check valve124 permits fluid to be sucked up from tank 37 into the upper cylinderchambers 46, 47 without shortcircuiting the flow of fluid through line72 when the pump 35 is pumping fluid through conduit 72 into one of theupper cylinder chambers 46, 47. Such shortcircuiting would be effectedif the necessary flow path for sucking up of fluid from tank 37 intochambers 46, 47 were provided in the form of a simple conduit, insteadof check valve 124. If a simple conduit were employed, then it would benecessary to control the flow of fluid in such conduit by some meansresponsive to the different positions of valves 16, 17 and furthermoreresponsive to operation and non-operation of pump 35. Evidently, suchcontrol means would be far more complicated than the simple check valve124. The use of the simple check valve 124, in the context depicted,permits the sucking of fluid into the upper cylinder chambers 46, 47when the tail gate descends or swings down solely under its own weight,without in any way interfering with the operation of the illustratedcontrol apparatus when the control apparatus is performing in any of theother four modes described above.

It may be desired to vary the pressure associated with pumping of fluidinto the upper cylinder chambers 46, 47 via conduit 72. For thispurpose, the flow restrictor 123 can either be made adjustable or elsebe constructed as a removable unit readily replaceable by a flowrestrictor having different characteristics.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofhydraulic circuits and constructions differing from the types describedabove.

While the invention has been illustrated and described as embodied in acontrol apparatus for a hydraulic-lift end gate of a moving van, or thelike, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In a hydraulic control apparatus for at least one double-actingconsumer of the type wherein at least one control valve includes atleast one valve member movable between first operative, second operativeand neutral positions to thereby respectively connect a firstfluid-conveying line of said consumer with a supply conduit which isconnected to a source of pressurized fluid, with a return conduit whichis connected to a tank, and to seal said first line from said conduits,and wherein said valve member of said control valve controls the flow offluid in a control conduit for a switchover valve which opens inresponse to fluid flow in said control conduit to provide a path for theflow of pressurized fluid from said supply conduit into a secondfluid-conveying line of said consumer, and wherein pressure-regulatingmeans is connected between the outlet of said switchover valve and saidtank and is operative for regulating the pressure of fluid in saidsecond fluid-conveying line of said consumer, the improvement consistingin that said pressure-regulating means comprises a flow restrictorconnected between the outlet of said switchover valve and said tank anda check valve connected in parallel to said flow restrictor with such anorientation as to permit flow of fluid from said tank into said secondfluid-conveying line of said consumer.

2. The apparatus defined in claim 1, wherein said pressure-regulatingmeans consists of said flow restrictor and said check valve.

3. The apparatus defined in claim 1, wherein said apparatus furtherincludes a pressure-limiting valve connected between said supply conduitand said tank for limiting the pressure of fluid in said supply conduit,and wherein the inlet of said switchover valve is connected to andreceives fluid from said supply conduit.

4. The apparatus defined in claim 3, wherein said pressure-limitingvalve and said flow restrictor and said check valve are incorporated ina common housing provided as a module.

5. The apparatus as defined in claim 1, wherein said flow restrictor isan adjustable flow restrictor.

1. In a hydraulic control apparatus for at least one doubleactingconsumer of the type wherein at least one control valve includes atleast one valve member movable between first operative, second operativeand neutral positions to thereby respectively connect a firstfluid-conveying line of said consumer with a supply conduit which isconnected to a source of pressurized fluid, with a return conduit whichis connected to a tank, and to seal said first line from said conduits,and wherein said valve member of said control valve controls the flow offluid in a control conduit for a switchover valve which opens inresponse to fluid flow in said control conduit to provide a path for theflow of pressurized fluid from said supply conduit into a secondfluid-conveying line of said consumer, and wherein pressure-regulatingmeans is connected between the outlet of said switchover valve and saidtank and is operative for regulating the pressure of fluid in saidsecond fluid-conveying line of said consumer, the improvement consistingin that said pressureregulating means comprises a flow restrictorconnected between the outlet of said switchover valve and said tank anda check valve connected in parallel to said floW restrictor with such anorientation as to permit flow of fluid from said tank into said secondfluid-conveying line of said consumer.
 2. The apparatus defined in claim1, wherein said pressure-regulating means consists of said flowrestrictor and said check valve.
 3. The apparatus defined in claim 1,wherein said apparatus further includes a pressure-limiting valveconnected between said supply conduit and said tank for limiting thepressure of fluid in said supply conduit, and wherein the inlet of saidswitchover valve is connected to and receives fluid from said supplyconduit.
 4. The apparatus defined in claim 3, wherein saidpressure-limiting valve and said flow restrictor and said check valveare incorporated in a common housing provided as a module.
 5. Theapparatus as defined in claim 1, wherein said flow restrictor is anadjustable flow restrictor.